Follow-up mechanism



Dec. l1, 1945.

N. l.. HAIGHT FOLLOW-UP MECHANISM Filed Jan. 16, 1942 Y ANDR;

Patented Dec. v11, 1.945

FOLLOW-UI MECHANISM Norman L. Haight, Glen Ridge, N. J., assignor toSperry Products, Inc., Hoboken, N. J., a corpo-v ration of New YorkApplication January 16, 1942, Serial No. 427,021

6 Claims.

This invention relates to electric follow-up systems wherein thedisplacement of a sensitive element with respect to a. follow-up membersetsv ample, in a magnetic compass the compass needle holds its positionon the magnetic meridian and if the ship moves there is a relativedisplacement between the ship and the compass needle. If a follow-upmechanism is set into motion to cause a follow-up member on the ship tobe restored to its original position with respect to the needle, thisangular movement between the member and the ship is a measure of therelative displacement of the ship with respect to the magnetic needle.The mechanism for operating the follow-up member to its originalposition through th'e angle of displacement may be caused to operaterepeater elements such as repeater compasses whereby the angulardisplacement of the ship with respect to the compass can be transmittedto remote points.

One of the diillculties which has heretofore been encountered inconnection with follow-up systems is that the motor which drives thefollowup element tends to cause the follow-up element to over-run, eventhough the impulse to the drivlng motor is theoretically zero when thefollowup member has returned to its original position with respect tothe sensitive element. This is due to the inertia. of the moving partsof the motor.

IThe over-running causes a displacement 'between the follow-up memberand the sensitive element in the opposite direction to the originaldisplacement, energizing the motor in the opposite direction and thussetting up an oscillation or hunting movement oi' the follow-up memberwith respect to the sensitive element. A corresponding hunting movementis set up in the repeater units. It is therefore one of the principalobjects of this invention to provide a follow-up mechanism in which suchhunting or oscillation will be eliminated and substantially dead-beatrestoring action by the follow-up motor of the follow-up element will beeffected.

The foregoing principal object of this invention may be accomplished bytaking into account not merely the relative displacement of thesensitive element with respect to the follow-up member, but also therate of displacement between said element and said member. I am aware ofth'e fact that various methods have been proposed for introducing a ratefactor in the operation of followup mechanisms, but these have allinvolved considerable complication. It is one ofthe objects of myinvention to introduce a rate factor which will involve the least amountof mechanism and the simplest arrangement. By this arrangement I am ableto accomplish two desirable results. First, I introduce a factor in themotor operation which will cause it to slow down at an accelerated rateas the follow-up member nears its original position with respect to thesensitive element so that over-running is prevented. Secondly, by thesame rate factor mechanism I am enabled to speed up the motor at anaccelerated rate during the interval that the follow-up member is movingaway from the sensitive element so that said motor will more quicklyoperate to return the member to its original position. Both th'espeeding up and the slowing down increments intr duced by this novelrate factor are in addition to th'e increments or speeding up andslowing down of the motor dependent upon magnitude of displacement.

In order that the motor shall more effectively be brought to restwithout over-running and h'ence causing hunting or oscillation, I mayprovide means for introducing into the motor a dynamic braking factor asthe follow-up element approaches its original position with respect tothe sensitive element and for removing such braking during the initialmovement of -the follow-up member away from the sensitive element so asto enable the motor quickly to restore the fgllowup member toward itsoriginal position.

Further objects and advantages oi this'invention will become apparent inthe following detailed description thereof.

In the accompanying drawing,

Fig. 1 is a wiring diagram of this invention.

Fig. 2 is a vector diagram illustrating the theory of the dynamicbraking.

Fig. 3 is a graph illustrating the theory of invention.

Referring to Fig. 1 of the drawing, I have shown my invention yappliedto a sensitive element indicated generally at Il which may carry acontactor element Il therewith and movable with respect to a follow-upmember indicated generally at I2. The invention is not limited to usewith any particular type of sensitive element but has generalapplication wherever a followup mechanism is used. Thus the sensitiveelement I0 may be the magnetic element of a magnetic compass holding itsposition on the magnetic meridian, while the follow-up member I2 may ibecarried by a ship and will therefore turn with the ship to causedisplacement between the sensitive element and the follow-up memberwhenever the ship turns from its When n the ship is travelling on itscourse, contact member II may be in engagement with mid-point Il of `s.potentiometer I l carried by the follow-up member I2.AbatryBisconnectedtothecenter point Il and to the outer points Il' andil' of the potentiometer to provide two circuits. The two branches I land Ii Vof the potentiometer have an equal number. of turns andtherefore the potential drops between point Il and ends of thepotentiometer contact arms, or between terminals II and Il and Il and Ilare equal. Since there is no relative displacement between contact armII of the sensitive element and point Il of the follow-up member I2, thefollow-up motor M which is geared to the follow-up member I2 throughsuitable gearing y2l is not effective to drive the gearing because'themotor is at rest. As'soon, however, as there is relative movementbetween the sensitive element Il and the .followup member I2 there willbe a difference in potential drop between terminals I1, Il and Il, Il.This difference in potential drop is caused to energize motor M in onedirection or the other, depending upon which potential drop I1. I8 orIl, I! is greater. In any case. the connections are such that the motorM is driven in the direction tov rotate follow-up member I2 so as tobring point I8 `of thepotentiometer again into coincidence with thecontact arm Il of sensitive element Il.

The control of motor M as outlined above is eifected by reason of thefact that motor M has a plurality ofiwindin, one of which, 2l, isnormally energiaed from a given circuit such as an ordinary 115 volt'.60 cycle circuit designed to -yield a vecim' indicated in Fig. 2 as Ei.The m0- insign. mtnispumsornuyutmnsnodlator indicated generally at Ilwhich may be en.

ergised from a source of 80 cycle alternating current and is providedwith two parallel circuits each of which contains a non-linear device inthe form' of a vacuum tube 4I, II' and impedances which may take theform of induction coils I2, 42' in inductive relation to a secondary 4I.The voltages from terminals I'I, Il and. It. Il maybe continuedtoterminals' I'I', Il' and Il', Il leading into the modulator Il. Thetwo non-linear'devices 4I, II' in combination with impedances such asthe transformer elements l2, I2' and 42 are arranged in such way as toproduce a voltage whose phase relationship coincides with that of vectorEi when the voltage drops between points Il', Il' and I2', I2' areequal. This is the case when -contact arm Il is in engagement withmid-point It ofthe potentiometer. 'I'he normal output from the moduslator when the voltage drop acrossv points I1', y

Il' equals 'the voltage drop across Il', Il', is

'appued to the winding :s after being passed through an ampliiler orother unilateral device A, and since the normal output results in avector of the same phase as Ei, this assists the dynamic braking of tiremotor. However, when there is relative movement between the follow-upmember and the sensitive element, and the voltage drop between I1'-, Il'differs from that between It', It', the modulator output is 90 out-ofphase with the normal output voltage due to the non torisise'desisnedtnat with an output from wind-f ing 2l of the phaseEithere is no rotation of the motor armature but only braking action. To.effect rotation of the motor it is necessary to introduce a vectorhaving a component ltsof a phase 90 removed fromthat of vector Ei andthe degree of rotation of tie motor will depend upon the degree of thevector En, while the. direction of rotation of the motor will dependupon the direction of vector Ez. Thus, if a vector lof the order E' isintroduced. the portion thereof in the direction of vector Es willdetermine 'the rate of rotation of the motor. It will also be observedthat the braking factor E1 has been reduced to tbepoint indicated at n.Thus. while the torque factor increases to motor M with the minimumbraking. However,

linear characteristics of the modulator which causes an unbalance' ofthe input. Thus an output is obtained in the direction of vector E: andthe result of combining the output Ea from winding 2t with the output Eifrom winding 2l is a vector E having a component Es which causesrotationof the motor and to a degree corre- 40 spending to thedimensions of the vector E4. At

E4, the braking factor diminishes. This result is desirable to obtainbecause' gagement with contact arm II.

the same time, the dynamic braking factor has been reduced Aby thedifference between the vectrsEi ndEa..

The voperation of the motor control thus described 'is as follows: whenthere is relative movement between the follow-up member I2 and thesensitive element III causing a voltage drop between I1', Il dinerentfrom thatbetween Il', Is', the modulator output on the winding 2l is 90out .of phase with the output of winding 2B.A

This produces a vector E' vwhich has a component Es which is the torquecomponent which produces rotation of the motor` in the proper directionto restore point Il of the follow-up member to en- Y The other componentof vector E is component Ei which is the dynamic braking factor. Thelarger the E:

when follow-up member I2 approaches its' initislposition with point I2in ent with contact arm Il, then the 'torque diminishes, and r as thetorque diminishes, the braking factor increases.Itwillthusbeseenthatbythe arrangement of two windings 90' out of phase,there is obtained a vector which follows a substantially circular pathindicated at 2l, the net result of which is to give diminishing. brakingas torque increases,v and, conversely, increasing braking as torque Forobtaining the .vectorasshowninll'ig.2,1utiliseamotorhaving a secondwinding 2l out of phasewith motor winding!! by '90 and cause thedifference in 4drop between terminals I1. Il and I2, I2 todeterminethedegree ofthevectorEsand angular movement of the component` the smallerthe dynamic braking factor Ei. This is desirable because when thedisplacement between the follow-up member and the l sensitive element islarge a large torque and small braking is required. However, when thepoint Il of the follow-up member approaches contact amil, the torquefactor E: diminishes and the dynamic braking factor increases until whenpoint I2 engages contact arm I I there is no output E: and the entireoutput of the modulator is in the direction'of Ei to give maximumbraking.

In addition to the dynamic brakingv factor introduced by the modulatoroutput which controls motor winding zt. u rate factor is introduced for.further guarding against the possibility of over-- running of the motorand hence of the followup member I2. The action of the follow-up memberin deviating from the sensitive member I 2,390,787 is illustrated inFig. 3. In the initial movementthe angular displacement and restore thefol-` low-up member to its original position. The portion of the graphillustrates theetfect of overrunning of the motor and consequent huntingmovement of the follow-up member to either side of the sensitiveelement, heretofore experienced in follow-up devices. The dynamicbraking of the motor described herenbefore will assist in achievingcurve i! but may not of itself be completely elective to prevent suchover-running. Therefore I have introduced a rate factor which willassist the motor in achieving the deadbeat action illustrated in graphportion 52. For this purpose the potentials between points II, I8 andIl, Il are parts of parallel circuits each of which includes aninductance ll, Il arranged so that the current from terminal I1 toterminal Il passes through inductance by way of cohdenser II while thecurrent from terminal I9 to terminal Il' passes through inductance 80'by way of condenser Il'. The inductances 60 and Il' are arranged inmutual inductive relation so that they act one upon tbe other, and areso wound that they are in opposition. Condensers I2, 62' and Il, I3' areintroduced in these parallel circuits. The rate at which inductance canbe fed from one side to the other is determined vto 'l volt drop betweenI1'. Il' and 3 volt drop between I8', I9', as an example. 'I'husI themutual inductance is eifective to increase the Ez factor which isapplied to the motor. in the initial stage 5I of the Fig. 3 graph. Thisis desirable in that it causes a quick return of the follow-up membertoward its original position. Having once caught up with the rate ofdisplacement and, in fact, started to return the follow-up member, themotor has reached the portion 52 of the graph of Fig. 3V and thus thereis a, decreasing rate of displacement between the follow-up member andthe sensitive element. Thus, if 4 volts represents the drop between Il,I9 and 6 volts the drop between II, I8, by reason of the mutualinductance between lill and i0' the decreasing rate of change mayincrease the voltage across II, I9 to 41/2 while decreasing the dropacross Il, Il to 5%. Thus the decrease in voltagediilerence between Il,I8 and I8, I9 is accelerated bythe mutual inductance with the resultthat the E: factor is diminished faster than would otherwise be the caseand the motor M is brought to rest more quickly than would otherwise bethe case as the point I3 of follow-up member I2 approaches contact arm II.

' In accordance with the provisions of the patent'statutes, I haveherein described the principle and operation of my invention, togetherwith the apparatus which I now consider to represent the best embodimentthereof, but I desire Y to have 1t understood that the apparatus shownby the natin'al frequency of oscillation of the enl tire system(including the six condensers, potentiometer, modulator, amplier, motor,etc).

Byreasonofthemutual inductances lI-andy Il' arranged in opposition, I amable to introduce into the motor M a rate factor which is beneilcial intwo directions, ilrst, to increase the rate of operation of the moto;lin the initial stage of displacement so as to cause the follow-up memberioretumasquieklyasposslbleandthen todecrease the rate of operation ofthe motor as the follow-up member nears its original position so as toprevent over-,running of the motor. This increase and this decrease areof course in addition to the increase and decrease which results fromthe increase and reduction in displacement and tly the increase andreduction in the E: vector applied to the winding .26.' Thus, forexample, in the initial stage of rapid displacement of the follow-upmember from the sensitive element, ilrst indicated by the portion'ill ofthe graph of Fig. 3, there will be an increase in voltl age drop betweenI'I, I8 and a decrease in voltage drop between Il, II. Were it not forthe mutual inductance between 6l and 6l this difference in potentialdrop would be exactly the same at I1', Il' and Il', Il' as at I1, Il andIl, I9. However, by reason of the mutual inductance, the `diminution lncoil Il' and the increase in coil Ilresultsinastillfurtherincreaseincurrent through'coil and a decrease incurrent through coil Il'. Thus, if normally when the system is inbalance there is a 5 volt drop acro I1, Il,

therewillbeaSvoltdropalsoacl-o Il, Il. If,

now displacement causes 'a 6 volt drop across I1, Il, there will be avolt drop across Il, Il. However, by reason of the mutual inductancebetweentlandtl'thisdiilexmcemaybeincreased is only illustrative and thatthe invention can be carried out by other equivalent means. Also, whileit; is designed to use the various features and elements in thecombination and relations described, some of these may be altered andothers omitted Without interfering Vwith the more general resultsoutlined, and the invention extends to such use.

Having described my invention, what I claim and desire to secure byLetters Patent is:

1. In a follow-up mechanism, a sensitive clement, a follow-up member, anelectric motor for actuating said member, said motor having an armatureand a plurality of windings, a source o! energy for normally energizingone of said windings so as to retard the armature, energization of theother of said windings in predetermined phase relationship with saidiirst winding serving to increase the retarding eiiect whileenergization of said second winding in different phase relationship withsaid first winding decreases the retard-- ing effect on said armatureand increases the torque thereof to the degree of said change in phaserelationship and in a direction depending on the direction of saidchange in phase relationship, means whereby said second winding isnormally energized in said predetermined phase relationship with saidrst winding when there is no relative displacement between saidsensitive element and said member, and means whereby relativedisplacement between said element and said member changes thepredetermined phase relationship of said second winding in a directionto cause said motor to reduce said relative displacement.

2. In a follow-up mechanism, a sensitive element, a follow-up member, anelectric motor for actuating said member, `said motor having an armatureand a plurality of windings, a source of energy for normally energizingone of said windings so as to retard the amature, energization of theother ofsaid windingsin phase with said ilrst winding serving toincrease the retarding effect retard the armature,` energlzation ofcreasing rate while energizati'on oi said second winding out oi phasewlthsaid rst winding decreases the retarding effect on 'said armatureand increases the torque thereof to the degree of said out-of-phaserelationship and in a direction depending on the direction of said phasedisplacement, means whereby said second winding is normally energized inphase-with said ilrst winding when there is no relative displace-mentbetween said sensitive eleJ ment and said member, and means wherebyrelative displacement :between said element and said member displacesthe phase of said second winding in a direction to cause said motor toreduce said relative displacement.

3. 'In a follow-up mechanism, a sensitive element, a follow-up member,an electric motor adapted td'be energized when said element and saidmember are relatively displaced, so as to restore said element and saidmember to undisplacedrelationship. said motor having an armature and apluralityvof windings, means for preventing over-running of said motor,said lastnamed means comprising a source of energy for normallyenergizing one of said windings so as to the `other of said windings inpredetermined phase relation- ,ship with said ilrstl winding serving toincrease ,potentialandsounkedasto the retarding eiiect whileenergization of said sec Y ond winding in different phase relationshipwith said winding decreases the retarding effect on said armature andincreases the torque thereof to the degree ot said change in phaserelationship and in a direction depending on the direction of saidchange in phase relationship, means whereby said second winding isnormally energized in said predetermined phase winding when there is norelative displacement means whereby relative, displacement between saidelement and said member generates a D. C. potential, means wherebychanges the predetermined said second winding in a direction tncause'said motor to` reduce 'said relative displacement, said last-namedmeans including mutual inductance means adapted to be rendered eiiectiveby the rate relationship with said ilrst' 'said D. C. potentialphaserelationship ot between said sensitiveelement and said member,

ment. a follow-up member,

o! change of said D. C. potential and so linked as ofchangeofsaidpotential." 4. In a, vfollow-up mechanism, a sensitive elel ment. afollow-up member. an electric motor .adapted to be energized when saidelement and 'to increase an increasing raie and decrease adesaidmemberarerelativelydisplaced,soastn ref store said element andsaid member to undi'splaced relationship. said motor having a pluralityof windings, means for preventing' over-running of said motor, saidlast-named means comprising asource of energy for normally energizingone o! said windings so as to retard the between said sensitive elementand said member,

means whereby relative displacement between said element and said membergenerates a D. C. potential, means whereby said D. C. potentialdisplaces the phase of said second winding in a dlrection to cause saidmotor to reduce said relative displacement, saidlast named meansincluding mutual` inductance means adapted to be rendered eiIective bythe rate of change of said D. C.

increase an increasing rate and decrease a decreasing rateo! change ofsaid ptential.

5. In a follow-up mechanism. ment, a follow-up actuating said member,means whereby relative displacement between said element and saidmeniber generates a D. C. potential. means a sensitive elemeansincluding a anced relative to each other, each circuit includ# ing aninductance, said .inductances being arranged in-mutually inductivevrelation.

In a follow-up mechanism, a sensitive eleactuating said member. meanswhereby relative, displacement between said element and said membergenerates a D. C.` potential, means whereby said potential actuates saidmotor. said last named means including a pair of circuits normallybalanced relative to each other, each circuit including an inductance,said induetances being arranged in mutually inductive relation andlinked in-opposition so as to increase an increasing rate 'and decreasea decreasing rate of cme of potenuti. y Y .Noms n maar. l

an armature and` retarding eiIect on said,

member,A an electric motor for whereby said potential actuates saidmotor. said last named pair of circuits normally balan `electric motorfor

